The life and performance of new and existing pipelines can be extended and optimised by lining lengths of metal pipe with polymer liners. Prior to their insertion in a host pipe, polymer liner pipes have a larger outer diameter than the inner diameter of the host pipe into which they are being inserted. The liner pipes are temporarily reduced in diameter immediately prior to insertion, for example by pulling them through the host pipe via a reduction die. After the insertion of the liner pipe is completed, the pulling tension is released and the liner pipe is allowed to revert towards its original size so as to provide a tight fitting liner inside the host pipe.
However, during the reversion process, the varying geometry of the inner diameter of the host pipe and the influence of any internal weld bead protrusions, surface irregularities and the like, may interfere with the reversion process, causing it to be uneven. In these circumstances, it is possible that air pockets may be trapped in the annular space between the outer surface of the liner pipe and the inner surface of the host pipe.
This is considered to present a potential operational risk that the liner pipe may collapse during operation of, say, a flowline which comprises lined pipeline. It is also considered to present a potential operational risk during initial laying of the lined pipeline—to the extent that it may not be considered safe to lay lined pipeline on the seabed using conventional methods.
Accordingly, it is an object of at least one aspect of the present invention to provide a method of laying lined pipeline that at least reduces the operational risks associated with laying lined pipeline on the seabed. Embodiments of aspects of the present invention are intended to increase the safety, integrity and reliability of the process and also of the resulting lined pipeline, and to obviate or mitigate one or more further disadvantages of existing methods.
Further aims and objects of aspects and embodiments of the invention will become apparent from reading the following description.